Carbonation of recycle liquor in sodium sesquicarbonate production



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United States Patent O CARBONATION F RECYCLE LIQUOR IN SODIUM SESQUICARBUNATE PRODUCTION Application May 4, 1953, Serial No. 352,955

7 Claims. (Cl. 23-63) This invention is an improvement on the process described in my United States Patent No. 2,346,140, issued April 11, 1944, and is a continuation-impart of application Serial No. 107,529, tiled January 29, 1949, now lPatent No. 2,639,217. 'My earlier invention relates to the production of pure sodium carbonate, specifically, sodium sesquicarbonate and soda ash, from Wyoming trona, or similar materials.- As described in said earlier patent, use is made of a recycling brine made up principally of a solution of sodium carbonate and bicarbonate in Water, the former greatly predominating in concentration. This brine is heated to at least about 185 F. and used to dissolve the raw trona. The hot solution is clarilied to remove shale, and is then subjected to treatment by 'an absorbent material, such as activated carbon, to remove organic and coloring matter. This matter imparts a yellowish color to the solution of tron-a, which is entirely removed by the use of a very small amount of activated carbon. The carbon is then removed by ltration and the Water-white solution cooled, thereby crystallizing out sodium sesquicarbonate of high purity and dead-White color. In said earlier patent, I have illustrated the use of eight stages of vacuum crystallizers, cooling the salt solution from about 185 F. to about 86 F. I also protected the recycled brine against the loss of CO2 by operating in closed vessels and providing an `atmosphere of CO2.

In application Serial No. 107,529, now Patent No. 2,639,217, I have disclosed that by modifying the process described in my prior patent to provide for the solution and crystallization of salt over a temperature range of about 212 F. to 140 F., and using open tanks for dissolving and taking no precautions to prevent loss of CO2, a substantial improvement in operation can-be realized. A certain loss of CO2 occurs in the process of said copending application due to decomposition of some of the sodium bicarbonate component of the recycling brine, but this is more than compensated for by other economies and advantages of the process described in said application.

In said application I have alsol disclosed that by bleeding or removing a certain percentage of the recycling brine in addition to that which is removed with the recovered crystals, it is possible to keep its concentrations of NaCl and Na2SO4, which are introduced with lthe trona and which tend to build up in the recycled brine, low enough so that the sodium sesquicarbonate crystals can be dried or calcined without washing, while producing a product of high purity. i

I have also `disclosed in said application that I may maintain the composition of the recycling mother liquor substantially constant and within the ratio of NazCOa to NaHCOa which will dissolve trona congruently and crys- `tallize out sodium sesquicarbonate by discarding from the recireulatiug system that amount of the mother liquor which is necessary to compensate for the CO2 lost and maintain the proper normal carbonate to bicarbonate ratio in the recrculating mother liquor.` This discarded mother liquor may be that normally lost by leakage or spillage from the circulating system; that adhering to the crystals which are preferably not Washed, but if washed, -only to ya limited extent; or may be a portion which is discarded to maintain the desired concentration of the mother liquor in contact with which sodium sesquicarbonate is the stable solid crystal phase, and which is yielded in substantial quantity upon cooling the hot mother liquor from the dissolvers from about 212 F. to about -F.

I have found that by contacting the recirculated mother liquor with the CO2 which is released in the evaporators -suicient of the CO2 may be recovered and sufficient of the NazCOs recarbonated to NaHCOs that the amount of mother liquor required to be discarded may be materially reduced.

While the contacting of the mother liquor with the CO2 released in the process may be carried out in various Ways, an efficient and economical way of recovering a part of the released CO2 is by direct liquid-gas contact of the cooled recirculating mother liquor with the escaping C02 in direct Contact spray condensers used in connection with the crystallizers, as described in my said copending application.

I may, if desired, also treat the bled or withdrawn or discarded portion of the recycling mother liquor for recovery of its carbonate values, notably, by carbonation with CO2 containing gas in a Well known manner, to precipitate most of the NazO present as relatively insoluble sodium bicarbonate, which is readily marketable, although treatment to recover the carbonate values of the bled olf portion is not necessary for the economical use of the process herein described.

It is, therefore, the object of my invention to provide au improved process for the recovery of sodium carbonate orl sodium sesquicarbonate fromv naturally occurring trona which will be more economic-al and less difcult to use than that described in my prior patent.

Another object of my invention is to provide a process for recovering sodium carbonate or sodium sesquicarbonate from trona which can be operated at higher temperatures than those described in my said prior Patent No. 2,346,140 without undue precautions against the loss or' CO2 from the circulating brine or without provisions for the addition of CO2 from outside sources to the circulating brine. i

Another object of my invention is to provide a method for the recovery of a part of the CO2 lost from ythe trona solution in the crystallizers, which comprises contacting the escaping CO2 with recircul-ating cooled mother liquor so that a portion of the CO2 is reabsorbed and a portion ot the recirculated mother liquor is recarbonated to NAHCOa to thereby partially restore the required NazCOs to NaHCOz ratio in the mother liquor.

Various -other objects and advantages of my invention Will appear as this description proceeds.

While the mol ratio of Na2CO3 to NaHCOa over which my process is workable depends in part upon the temperature of solution and crystallization and the amount of dissolved impurities in the circulating mother liquor, in general this mol ratio should be maintained between the limits of about 1.7 mols NazCOs to 1 mol NaHCOs' and 5.8 mols NazCOs to 1 mol NaHCOs in the hot mother liquor entering the crystallizing step at about 212 F. In the cooled mother liquor leaving the crystallizers at about 140 F., the mol ratio corresponding to 1.7 mols.

yields of sodium sesquicarbonate become so small as to be negligible and other compounds'than the-sesquicarlatented Feb.` 5, 1957.l

bonate begin to crystallize out. Therefore, when, due to the loss of CO2 from the circulating liquor in the dissolving, clarifying and crystallizing steps, the mol ratio of NazCOs to NaHCOgl in the mother liquor falls materially outside of the ranges given above, it is economically desirable to `correct the composition of the mother liquor by bleeding or discarding sufficient of the mother liquor that the amount of NaHCOs added in dissolving trona will maintain the desired balance. However, it is one of -the objects of my invention to choose a desirable composition ofthe mother liquor at the start and to maintain this composition in as steady a state as possible and 'in the manner hereinafter specified for the carrying out of my process.

Referring now to the drawings, Fig. 1 illustrates a diagrammatic outline of the process, and Fig. 2 is a part sectional View on a larger scale diagrammatically illustrating one form of direct contact spray condensers which may be used in connection with the crystallizer.

In the drawings, represents an agitating vessel for dissolving ground trona in recycled brine which has been heated in 11 to about 212 F. I preferably grind the trona so that all will pass a 20 mesh screen. Two or three dissolving vessels may be used in series so as to make a substantially saturated solution, or this may be done by dissolving in batches in a well known manner, as may be preferred. The saturated solution then goes to 12, which is preferably a four-tray parallel feed thickener, insulated heavily against the loss of heat. The

thickened underfiow of this thickener passes to a centrifuge 13, or other well known suitable dewatering device, in which shale and other insoluble material found in natural trona is removed. The brine removed in 13 joins the clarified overow from 12 and the insoluble residue is discarded to waste. I may employ all or a part of the makeup water referred to later, to wash the insoluble material in 13 free of brine, and return this wash to the main stream of makeup water.

The combined streams of recycled brine from 12 and 13 go to an agitating treating tank 14 where the brine is retained about half an hour in agitated contact with activated adsorbent carbon, in amount corresponding to about .3% of the trona introduced. This treatment also may be done either in continuous flow or batches. This treatment removes organic and coloring matter and after the recycled brine is filtered in 15, a water-white solution results which is quite free from iron. and will not foam in the vacuum crystallizers. The spent adsorbent removed from filter 15 may be discarded or revived for reuse.

The clarified hot saturated brine now enters the first effect of a series of vacuum crystallizers, 16a, b and c. I prefer to employ three crystallizers in series, which is the number shown in the drawings. However, the number of crystallizer effects is dictated by considerations of economy and I may carry out my process, if desired, with the use of a single effect. Up to this point no precautions have been taken to prevent the loss of CO2 from the hot trona solution in vessels 10, 12, 14, etc.

In the crystallizers 16a, 16h and 16e a separate recirculation of brine is preferably maintained through each effect by withdrawing a slurry of brine and crystals through a barometric leg 17 from the bottom of each effect, aud pumping it back by pumps 18 into the main bodies of the effects. The circulating brine from 15 enters the recirculation of the first effect at 19 and leaves at 20, entering the recirculation of the second effect at 21 and leaving at 22, entering the recirculation of the third effect at 23 and leaving at 24, whence it is pumped into crystal settler 25.

The amount of recirculation just referred to in each effect may be controlled by theoperator within limits, and this in turn controls the so-called flash range of the vacuum crystallizers. The fiash range is the difference in temperature between that prevailing in the crystallizer and that of the mixture of the recirculating feed, and the net feed to each crystallizer. For example, according to one set of operating conditions, the feed entering the first effect at 19 is at a temperature of about 212 F., leaving at 188 F., showing a temperature drop of 24. The feed entering the second effect is at 188 F., and leaving isr at 164 F., likewise showing a drop in the effect of 24. The feed entering the third elfect is at 164 F., leaving at 140 F., likewise showing a drop of 24. Therefore, when operated according to these conditions, there is a net temperature drop of 24' in each of the three effects of the crystallizers. A flash range in each crystallizer effect may be chosen over a wide range from, say 1 F. to 7 F. For'. the purpose of this description it will be assumed that the ash range is 4 F. This is just j/6 of the total temperature drop so, in this example, the. recirculation pulse the net` feed entering the crystallizer' must be six times as great as the net feed itself. This means that the recirculation must be five times the net circulation through each effect.

In this example, the pressure in the third effect is maintained at about 5" Hg absolute, about 10 Hg absolute in the second effect, and about 19 Hg absolute in the first effect.

It is to be. understood, however, that different sets of operating conditionsr may be chosen and maintained and that a greateror lesser number of crystallizer effects may be used.

In each of the crystallizers 16a, 16b and 16C, some CO2 will be flashed off from the brine which, for example, enters the recirculationl of crystallizer 16a at a temperature of about 212 F. and is subjected to the vacuum prevailing in this crystallizer. A portion of the CO2 which flashes off in the crystallizers 16a and 1Gb is recovered by contacting the escaping CO2 with cooled recirculating mother liquor in the jet condensers 26 and 27 in which, as illustrated diagrammatically in Fig. 2, the steam and CO2 enters at 40, the recirculating mother liquor enters at 39 and the gases flow counter-current through the sheets of mother liquor (indicated in dotted lines) to the outlet leading to vacuum pumps 29.

As described' in my copen'ding application, now Patent No. 2,639,217, the separate effects 'are each provided with jet condensers 26, 27 and 28. Each condenser is provided with a top connection to a vacuum pump 29 for removing unabsorbed` CO2, 4and any other non-condensable gases, land each is provided with a barometric leg 30. Condenser 28, which is connected to the third, or last, effect of the series of: crystallizers, is preferably supplied with a spray of pure water at a maximum temperature of about F. The'water which is evaporated in this effect under the influence of the vacuum, is condensed and returned'to the circulation at 31 at a temperature of about F. Cold pure makeup water, some of which may have been used as a wash in 13, is introduced at 32. I find it preferable to introduce the water in the region of 31 `and 32 because this immediately removes the saturation of the yrecircul'ating brine and cools the brine to some extent, and from that point in its iiow until it again reachesvessel 10, it is unsaturated and cannot, therefore, depositcrystals'in the pipe lines. The balance of the water introduced into condenser 28, amounting to about 950 G. P. M. is cooled in tubular cooler .33, on the outside of the piping of which flows cold untreated water from a spray pond, or tower, not shown. In this way the treated water which is evaporated'in the third effect is saved and returned to the system. Whereas, if the condenser 23 had been provided with untreated water, the pure water would have been contaminated by untreated water.

I have pointed out that the net circulation from the third effect 16e iswithdrawn at 24 and pumped to settler 25. The underflow from 25 is a thickened slurry of crystals of sodiumI sesquicarbonate, which is dewatered' in a vacuum filter or centrifuge 34. I prefer not to wash these crystals when using my process to treat the Green River, Wyoming trona, or at most to wash them only partially, because the content of NaCL, Na2SO4 and other soluble salts in this trona is so low that withdrawing a very :small part of the circulating brine 'at 35, `as shown, together with the brine remaining with the crystals from 34, I keep the concentration of NaCl and NazSOt in the recycling brine at so low a level that the amount of these materials added to the sodium sequicarbonate crystals by the adhering brine is within permissible limits to allow this product to be classed as chemically pure. In order to `accomplish this end, however, I iind it desirable to treat the water of the Green River region, which is used for makeup, by ion exchange or other suitable treatment in order to remove Na2SO4 `and NaCl from it before it is used in the process.

It should be understood that spillage and other losses of the recirculating brine in a process of this type, notably with the unwashed or only partially washed crystals of sodium sesquicarbonate, may be such that a constant withdrawal at 35 is not required, and that if the concentration of NaCl and Na2SO4 builds up in the circulation, and if due to a too great loss of C02 the composition of the recirculating mother liquor changes to the point where trona is no longer congruently soluble and sodium sesqui- Vcarbonate is not the only solid crystal phase, suicient of the recirculating brine may be withdrawn at 35 to keep the recirculation in the required balance. Although this withdrawal may be done periodically, it is better to establish it continuously so as to maintain the recirculation in the steady state of desired concentration.

The product of my process, which is substantially pure sodium sesquicarbonate, NazCOa-NaHCOa-ZHzO, may be calcined in any suitable device 36, to make soda ash of high purity or may be `dried in drier 37 to produce highly pure crystals of sodium sesquicarbonate. The

brine withdrawn at 35 may be treated with CO2 in 38 to recover most of its Na as sodium bicarbonate. However, the amount of the latter thus recovered, is relatively small `and I may, if I prefer, discard the withdrawn brine without serious economic loss.

The overow from the settler is at a temperature of about 140 F. This temperature is lowered and the brine is somewhat diluted by the `addition of makeup and recovered water at 31 and 32, as disclosed above. This brine is then used as the condensing spray in barometric condenser 27 which serves the second effect. This some- Wh'at further dilutes and heats the brine which is then used as the condensing spray in 26. The brine leaving 26 through the baromet-ric leg 30 may be heated as high as 165 F., and is the recycled mother liquor which goes to heater 11 preparatory for reuse for dissolving trona in 10.

The cooled recycling mother liquor containing dissolved NazCOa and NaHCOa is Idirectly contacted with the CO2 gases escaping from the crystallizers 16a and 16b in the condensing sprays in condensers 27 and 26, and thereby absorbs a portion of the CO2 and is partially recarbonated by the reaction.

thus reducing the NazCOa content and increasing the NaHCOa of the mother liquor so as to partially compensate for the loss of CO2 in the process and partially restore the desired NazCOs, NaHCOa ratio in the mother liquor.

As shown in Fig. 1 of my earlier patent, No. 2,346,140, this recycled mother liquor, in order to dissolve tron'a congruently and to crystallize sodium sesquicarbonate from the solution by cooling to 30 C. (86 F.), may have a composition of about 23.5 gms. NazCOa and 5 gms. NaHCOz per 100 gms. H2O, corresponding to a ratio of 3.7 mols NazCOa to 1 mol NaHCOa; and by interpolation at 140 F., about 28 gms. NazCOs and 8.5

gms. `NaHCOs per gms. H2O, in turn corresponding to a ratio of 2.6 mols NazCOa to l mol NaHCOs. In the calculations which follow, pertaining to the example of the present application, the composition of the motor liquor used to dissolve Vthe trona is given as 28.4 gms. NazCOs and 7.7 gms. NaHCOa per 100 gms. H2O.

When using F. as the temperature of crystallization, or the temperature at which the solution leaves the crystallizer, Fig. l of the earlier patent, would have a practical range of composition from about 27 gms. NazCOa and 9.5 gms. NaHCOa to 100 gms. H2O, to about 36 gms. NazCOa and 5 gms. NaHCOa per 100 gms. H2O, in turn corresponding to about 2.25 mols NazCOa per mol of NaHCOa, and 5.7 mols NazCOs per mol NaHCOa.

While a considerable variation is to be noted in the above figures, this constitutes no diiculty because a considerable range of composition is allowable while still maintaining congruent solution of the trona and recrystallization of sodium sesquicarbonate by cooling as the stable solid crystalline phase. Once |having established |a mother liquor of given composition at one point in the recirculation, as for example, the mother liquor used to dissolve the tron'a, my present invention leads to the maintenance of this composition preferably as a steady state with maximum degree of economy.

In the process described, there are several points at which CO2 is lost by decomposition of the sodium bicarbonate of the circulating brine, notably from the dissolver 10, the thickener 12, and from the discharge of each of the vacuum pumps 29. Therecovery of CO2 in the condensers 26 and 27, however, partially reduces this loss and reduces the amount of Withdrawal necessary at 35 so that this withdrawn brine taken together with the brine which adheres to the crystals, which is also withdrawn because the crystals are not Washed, can be balanced with the lost CO2 with less discard than would be necessary if there were no recovery of CO2 in the condensers 26 and 27. As I add trona and Water to the cycle, I therefore keep the NaHCOs and'NazCOs within the desired ratio Without having to control the ratio by adding CO2 from other sources to recarbonate the mother liquor or by adding calcined soda ash to the circulating brine. I have found that my discovery and application of this relationship leads to greater economy and ease of control in the operation of the process as compared with my earlier invention.

In what follows I shall set forth the approximate data concerned with producing 100,000 tons soda ash annually, and, on the assumption that half the evolution of CO2 occurs in the crystallizers and that two-thirds of the CO2 ashed off in the crystallizers is recovered in the condensers 26 and 27, I shall show the approximate loss of CO2 which would occur if there was no recovery in the condensers 26 and 27. The exact amount of CO2 recovered in the condensers cannot be accurately determined but it is known that the amount of CO2 lost in my process is less than the amount of loss which theory would lead one to expect.

Example A representative analysis of the Wyoming trona is as follows:

Constituent NzBtO c The composition of the mother liquor used to dissolve thc'trona is preferably about as follows:

Lbs. of trona treated per hour 39, 300 Weight of dry crystals NazC ;.NaHC 03.2H2O produced, lbs/hr. 37, 400 Lbs/hr. recyeled mother liquor:

aHCV 3 14,600 NazCOs 54, 600 NaCl 1,400 NagSOA 570 Water. 208,000

Total, approximately 278, 000

With Without Partial Recovery Recovery o CO2 in of CO1 in Condensers Condensers Mols per hr. CO2 lost 2. 68 4. 02 Lbs.lhr. CO2 lost 11s 177 Lbs/hr. NazCOa in the brine withdrawn and with the crystals to give a trona analysis with the NaHCO3 in the brine and with the lost CO: 1,297 1,930 NaHCOz in brine Withdrawn and with crystals, lbs./hr 351 517 H2O withdrawn and with crystals, lbs/hr. 4, 570 6, 800 Water with sodium sesquicarbonate crystals,

lbs/hr. (this is a constant) 3, 930 3, 930 Water withdrawn, lbs/hr. (This is a variable to match the loss of CO2. If the latter increases, the amount Withdrawn also increases.) 640 2, 870

The amount of NaCl added with the trona is 33.6 lbs/hr. and as this must be removed with the Water withdrawn and in the crystals, the concentration of NaCl, expressed as lbs. NaCl per 100 lbs. Water, is

Same concentration for NagSOi .306 NaCl in soda ash (this results from the NaCl in the mother liquor adhering to the crystals el sodium sesquicarbonate) percent 111 Same for NazSOi .047

Total material in brine adhel g to unwashed crystals, lbs./h

NAHCOL 303 NagCO3 1, 115 Equivalen odiuin sesquicarbonate 1,860 Equivalent percentage of total prodnced 5. 0

aCl. 28.9 NaiSO 12.0 H2O` 3,930

The circulating brine withdrawn contains the following lbs/hr.:

With -Without Partial Recovery Recovery of O02 in ol CO2 in Condensers (This loss is so small where CO; is partially recovered in the condonsers that recovery by carbonation, as indicated in 38, is entirely optional) Molratio, NanCGa/NaHCO; 1.035 (This is a satisfactory ratio, comparing as it docs with 1.0 in

pure sodium sesquicarbonate.) Makeup water, lbs/hr. (including that withdrawn and with the crystals, plus about 2,000 lbs/hr. lost with the vrastc from iilter 13 and with the adsorbent from filter 15) 5, 570 Pure Water returned to process from condenser 28, lbs. 11,040 Lbs. Water per hr. which must be heated from about 165 to 212 F. (this is the amount entering the crystal settler 25,

plus makeup plus water returned from condenser 28) 208, 000 B. t. u./l1r. tohcat Water 0, 780, 000 li. t. u./hr. to heat solids in solution 810,000 Total B. t. u./hr 10, 590,000

To this must be added the fuel required to calcine the vcrystals of sodium sesquicarbonate or to dry them.

Summing up, in the practice of my process, when the loss of CO2 is 118 lbs/hr., I Withdraw suiiicient of the 8 circulating brine so that with the brine which adheres to the unwashed crystals, I have withdrawn the following lbs/hr.:

The 118 lbs/hr. CO2 would react with Na2CO3 as follows:

Na2CO3-I-COZ-I-H20- ZNaHCO3 and if this reaction were actually allowed to occur, it

would use up about 284 lbs. NazCOs, and make 451 lbs. NaHCOs. This wouldV give:

NaHCOs 800 Na2CO3 1009 Weight ratio, NaHCO3/Na2CO3=.79.

This same ratio occurs in trona, which shows that I have virtually operated my process with depletion only of trona and water, together with the NaCl and Na2SO4 introduced with the trona, and that because I also introduce trona and water into the circulation, I therefore may operate the process continuously with substantially unvarying composition of the circulation, with minimum losses, maximum yield, and a product of the highest purity.

While I have described a prefer-red method of practicing my invention it will be understood that various modications andA changes may be made from that described without departing from the spirit of my invention or the scope of the appended claims.

I claim:

l. A process for the production of sodium sesquicarbonate from crude trona which comprises dissolving the trona in a circulating system open to the atmosphere at the point where the trona is dissolved, in a recirculating solution of a mother liquor of sodium carbonate and sodium bicarbonate in which the ratio of normal carbonate to bicarbonate is maintained so that the normal carbonate and the bicarbonate in the trona are dissolved in the ratio in which they exist in the trona at a temperature not substantially less than the boiling point of the recirculating solution, with consequent loss of CO2 from the circulating system at the point where the trona is dissolved, crvstallizing and separating sodium sesquicarbonate from said solution by cooling, and recovering a portion of the CO2 lost in the crystallizers by passing it through a stream of cooled recirculating mother liquor and discharging the unabsorbed CO2 to the atmosphere.

2. A process for the production of sodium sesquicarbonate from crude trona which comprises dissolving the trona in a circulating system open to the atmosphere at the point Where the trona is dissolved, in a recircnlating solution of a mother liquor of sodium carbonate and sodium bicarbonate in which the ratio of normal carbonate to bicarbonate is maintained so that the normal carbonate and the bicarbonate in the trona are dissolved in the ratio in which they exist in the trona at a temperature not substantially less than the boiling point of the recircuiatfing solution, with consequent loss of CO2 from the circulating system at the point where the trona is dissolved, crystallizing and separating sodium sesquicarbonate from the mother liquor by cooling, diluting the mother liquor with makeup water and recirculating the mother liquor, and recovering a portion of the CO2 lost in the crystallizers by passing it through a stream of cooled recirculating mother liquor and discharging the unabsorbed CO2 to the atmosphere.

3. The method of producing refined sodium sesquicarbonate from naturally occurring trona carrying insoluble material and coloring matter, which comprises dissolving the trona in a circulating system open to the atmosphere at the point of dissolution of the trona in a recycling brine of sodium carbonate and bicarbonate at a temperature of not substantially less than the boiling point of the recirculating solution with consequent loss of CO2 from the recirculating solution, removing the insoluble material from said solution, contacting the solution with an adsorbent and removing the adsorbent and coloring matter from said solution, crystallizing and separating sodium sesquicarbonate by cooling, and recovering a portion of the CO2 lost in the crystallizers by reacting it with the cooled recirculating mother liquor, discharging the unreacted CO2 to the atmosphere and maintaining the ratio of concentrations of sodium carbonate and sodium bicarbonate in the recycling solution at the desired amount by withdrawing from the solution, including the solution remaining with the crystals of sodium sesquicarbonate, the stoichiometric amount corresponding to the net amount of CO2 lost, and recycling the remaining solution to dissolve more trona.

4. The method of producing refined sodium sesquicarbonate from naturally occurring trona carrying insoluble material and coloring matter, which comprises dissolving the trona in a circulating system open to the atmosphere at the point where the trona is dissolved in a recycling brine of sodium carbonate and bicarbonate at a temperature of not substantially less than the boiling point of the recirculating solution with consequent loss of C02 from the recirculating solution, removing the insoluble material from said solution, contacting the solution with an adsorbent and removing the adsorbent and coloring matter from said solution, crystallizing and separating sodium sesquicarbonate by cooling, and recovering a portion of the CO2 lost in the crystallizers by reacting said CO2 with the cooled recirculating mother liquor by passing the CO2 which is released in the crystallizers through direct contact spray condensers in which the condensing liquid is cooled recycling brine discharging from the circulating system the unreacted CO2 passing through the spray condensers, and maintaining the ratio of concentrations of sodium carbonate and sodium bicarbonate in therecycling solution at the desired amount by periodically withdrawing from the solution, including the solution remaining with the crystals of sodium sesqnicarbonate, the stoichiometric amount corresponding to the net amount of CO2 lost, and recycling the remaining solution to dissolve more trona.

5. A process for the production of sodium sesqnicarbonate from crude trona which comprises dissolving the trona in a circulating system open to the atmosphere at the point Where the trona is dissolved, in a recirculating solution of a mother liquor of sodium carbonate and sodium bicarbonate containing a concentration of normal carbonate to bicarbonate between 1.7 and 12.6 mols of normal carbonate to 1 mol of bicarbonate, at a temperature not substantially less than the boiling point of the recirculating solution with consequent loss of CO2 from the circulating system, crystallizing and separating sodium sesquicarbonate by cooling, recovering a portion of the CO2 lost in the crystallizers by passing the CO2 lost in the crystallizers through direct contact spray condensers in which the condensing liquid is cooled recirculating mother liquor, and reacting a portion of said CO2 with the recirculating mother liquor to increase the sodium bicarbonate content of the recirculating mother liquor and maintaining the ratio of concentrations of sodium carbonate and sodium bicarbonate in the recycling solution at the desired amount by periodically withdrawing from the solution, including the solution remaining with the crystals of sodium sesquicarbonate, the stoichiometric amount corresponding to the net amount of CO2 lost, and recycling the remaining solution to dissolve more trona.

6. A process for the production of sodium sesqnicarbonate from crude trona which comprises dissolving the trona in a circulating system open to the atmosphere at the point where the trona is dissolved, in a recirculating solution of a mother liquor of sodium carbonate and sodium bicarbonate containing a concentration of normal carbonate to bicarbonate between 1.7 and 12.6 mols of normal carbonate to l mol of bicarbonate, at a temperature not substantially less than the boiling point of the recirculating solution with consequent loss of CO2 from the circulating system, crystallizing and separating sodium sesquicarbonate from the mother liquor by cooling, diluting the mother liquor with makeup water and recirculating the mother liquor and recovering a portion of the CO2 lost in the crystallizers by passing the CO2 lost in the crystallizers through direct contact spray condensers in which the condensing liquid is cooled, diluted, recirculating mother liquor, reacting a portion of said CO2 with the recirculating mother liquor to increase the sodium bicarbonate content of the recirculating mother liquor, discharging CO2 unabsorbed in the recirculating liquor from the circulating system, and maintaining the ratio of concentrations of sodium carbonate and sodium bicarbonate in the recycling solution at the desired amount by withdrawing from the solution, including the solution remaining with the crystals of sodium sesquicarbonate, the stoichiometric amount corresponding to the net amount of CO2 lost, and recycling the remaining solution to dissolve more trona.

7. A process for the production of sodium sesqnicarbonate from crude trona which comprises dissolving the trona in a circulating system open to the atmosphere at the point where trona is dissolved in a recirculating solution of sodium carbonate and sodium bicarbonate at a temperature not substantially less than the boiling point of the recirculating solution with consequent substantial loss of CO2 from the circulating system, said solution containing a greater concentration of the normal carbonate than of the bicarbonate but a concentration thereof at which sodium carbonate and sodium bicarbonate are dissolved in the solution in the ratio in which they exist in trona, crystallizing and separating sodium sesqnicarbonate by cooling, maintaining the ratio of concentrations of sodium carbonate and sodium bicarbonate in the recirculating solution substantially constant by reacting a portion of the CO2 lost from the circulating system with the cooled recirculating solution to increase the sodium bicarbonate content of said solution and by Withdrawing from the circulation the stoichiometric amount of solution corresponding to the amount of unreacted CO2 lost to restore the desired sodium carbonate to sodium bicarbonate concentration, and recirculating the remainder of said solution of sodium carbonate and sodium bicarbonate and dissolving more trona therein.

References Cited in the tile of this patent UNITED STATES PATENTS 1,319,128 Watson Oct. 21, 1919 1,618,834 Kuhnert Feb. 22, 1927 2,346,140 Pike Apr. 11, 1940 2,414,607 Phillips Jan. 21, 1947 2,420,795 Phillips May 20, 1947 2,639,217 Pike May 19, 1953 2,656,245 Gray et al Oct, 20, 1953 

1. A PROCESS FOR THE PRODUCTION OF SODIUM SESQUICARBONATE FROM CRUDE TRONA WHICH COMPRISES DISSOLVING THE TRONA IN A CIRCULATING SYSTEM OPEN TO THE ATMOSPHERE AT THE POINT WHERE THE TRONA IS DISSOLVED, IN A RECIRCULATING SOLUTION OF A MOTHER LIQUOR OF SODIUM CARBONATE AND SODIUM BICARBONATE IN WHICH THE RATIO OF NORMAL CARBONATE TO BICARBONATE IS MAINTAINED SO THAT THE NORMAL CARBONATE AND THE BICARBONATE IN THE TRONA ARE DISSOLVED IN THE RATIO IN WHICH THEY EXIST IN THE TRONA AT A TEMPERATURE NOT SUBSTANTIALLY LESS THAN THE BOILING POINT OF THE RECIRCULATING SOLUTION, WITH CONSEQUENT LOSS OF CO2 FROM THE CIRCULATING SYSTEM AT THE POINT WHERE THE TRONA IS DISSOLVED, CRYSTALLING AND SEPARATING SODIUM SESQUICARBONATE FROM SAID SOLUTION BY COOLING, AND RECOVERING A PORTION OF THE CO2 LOST IN THE CRYSTALLIZERS BY PASSING IT THROUGH A STREAM OF COOLED RECIRCULATING MOTHER LIQUOR AND DISCHARGING THE UNABSORBED CO2 TO THE ATMOSPHERE. 